react-with-hooks | Ponyfill for the React Hooks API | Frontend Utils library

1. Trying to update something should be done in a put request, not a post request. This is a REST API convention, but a discrepancy may have some consequence down the line.
2. In this case, the error in your development tools is telling you that one of your components has an onChange/onSubmit etc property that is changing over the course of one mount from null to a function. This is not what's causing your issue, but I suspect it can be fixed by declaring the code in a handleSubmit function and then putting that into your onSubmit.
3. I think the error that's actually causing your problem is that the updatedTodo is not being sent to the backend. All that is being sent is the id (second parameter of axios.post). So if you pause the backend during execution, you would see that request.data = the id only, when it should be TodoSerializer's readable fields.

PS:

1. You can add a "debugger;" statement in the code after the updateToDo async request error to see what the error actually is (read more on the development tools debugging - browser dependent).
2. Don't abuse fragments - in this case, it would make for a more accessibility-friendly experience if you use divs in most of these components. Wouldn't it make more sense if the heading of some content was grouped with the content? https://developers.google.com/web/fundamentals/accessibility/focus/dom-order-matters